A phosphorous-based bi-functional flame retardant for rigid polyurethane foam

A bi-functional flame retardant for rigid polyurethane foam (RPUF), denoted as PDEP, was designed and synthesized. PDEP contained two phosphorus-based moieties: phosphophenanthrene (DOPO) and a phosphate (DEP), which may exert different functions at different temperatures. DEP and DOPO moieties in sequence decomposed with increasing temperature, continuously releasing and holding high-content phosphorus-oxygen free radicals with quenching effect and producing viscous residues to bond and integrate other char species leading to high barrier effect. The flame retardant modes of action of PDEP was confirmed by experiments using thermogravimetric analysis-Fourier transform infrared (TGA-FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), FTIR and SEM. PDEP was incorporated into RPUF system via co-cured with other polyol components. Using expandable graphite (EG) as additive-type flame retardant, an enhanced flame retardancy in RPUF was observed.